New optical/uv counterparts and SEDs of Isolated NS ATISH KAMBLE, D. KAPLAN (UW-MILWAUKEE), M. VAN KERKWIJK (TORONTO) AND W.

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1 New optical/uv counterparts and SEDs of Isolated NS ATISH KAMBLE, D. KAPLAN (UW-MILWAUKEE), M. VAN KERKWIJK (TORONTO) AND W. HO (SOUTHAMPTON)

2 RX J a puzzle! Featureless BB spectrum instead of harder than Wien tail or any spectral features (Burwitz et al 2001, 2003) Optical excess = 8 (Walter & Matthews 1997; van Kerkwijk & Kulkarni 2001) but Rayleigh-Jeans Fλ (erg/s/cm 2 /Å) XMM CXO WFPC2/F170W WFPC2/F300W WFPC2/F450W WFPC2/F606W X-ray => Too small Radii Wavelength (Å) Optical => too large Radii (Braje & Romani 2002)

3 Is RX J1856 special or do all INSs show similar behavior (Optical Excess, Rayleigh- Jeans spectrum)? Could this behavior be explained?

4 Identifying counterparts easy HST photometry => very reliable 4

5 easy Identifying counterparts some-what easy

6 Identifying counterparts easy some-what easy difficult Mignani et al. 2009

7 Identifying counterparts optical

8 Identifying counterparts optical UV Estimated proper motions => consistent with Motch et al. (2005, 2009)

9 10 12 CXO XMM Fλ (erg/s/cm 2 /Å) WFPC2/F170W WFPC2/F300W WFPC2/F450W WFPC2/F606W Wavelength (Å)

10 5 FUVMAMA F25SRF2 F140LP F170W F25QTZ F300W F450W F475W 50CCD F606W F28X50LP Cooler WFPC2/F170W CXO WFPC2/F450W WFPC2/F606W WFPC2/F300W XMM Fλ (erg/s/cm 2 /Å) Wavelength (Å) power law with index : opt excess : 5-50 power law might be too simplistic => lines/ wings (Pavlov s talk PSR0656) log10 [λ 4 Fλ (Å 4 erg/s/cm 2 /Å)] Wavelength (Å) Hotter

11 Different emission regions : Pulsed fraction v/s Optical Excess 25 Braje & Romani 2002, Kaplan et al Pulsed Fraction (%) Pulsed Fraction (%) Optical Excess Optical Excess small hotspot => large pulsed fraction and optical excess : No strong correlation

12 Different emission regions : Opt/UV as separate BBs Braje & Romani 2002, Kaplan et al RX J2143 RX J1605 ROUV/RX 10 RX J1308 RX J0720 RX J0806 RX J1856 RX J0420 Dotted lines : unabsorbed BB T OUV /T X

13 Different emission regions : Pulsed fraction v/s Optical Excess Braje & Romani 2002, Kaplan et al small Hotspot => large pulsed fraction and optical excess : No strong correlation Separate BB : Unreasonably high radii for NS Spectral Index Rayleigh-Jeans 3 spectral-index v/s kt : 2.8 Hotter objects have 2.6 smaller spectral index kt (ev)

14 Magnetospheric emission : non-thermal Lum-X v/s Edot Isolated Neutron Stars Rotation Powered Pulsars NT Lum-X of INSs are close to 100% of Edot. Comparatively, radio pulsars have NT Lum-X = 10^-3 x Edot (Becker & Trumper 1997) Log(Luminosity : kev) (erg/s) Log(Edot) (erg/s)

15 Magnetospheric emission : Lum-opt v/s Edot NT Lum-X of INSs are close to 100% of Edot. Comparatively, radio pulsars have NT Lum-X = 10^-3 x Edot (Becker & Trumper 1997) Lum-Opt of INSs are >10^-3 x Edot. Radio pulsars have Lum-Opt <10^-6 x Edot (Zalin & Pavlov 2004) Log(Optical Luminosity) (erg/s) Isolated Neutron Stars Rotation Powered Pulsars Log(Edot) (erg/s)

16 Magnetospheric emission : Optical Excess v/s Edot NT Lum-X of INSs are close to 100% of Edot. Comparatively, radio pulsars have NT Lum-X = 10^-3 x Edot (Becker & Trumper 1997) Lum-Opt of INSs are >10^-3 x Edot. Radio pulsars have Lum-Opt <10^-6 x Edot (Zalin & Pavlov 2004) Optical Excess If part of the optical emission is due to spin down => Optical Excess - Edot correlation : No such definitive correlation is seen Log(Edot) (erg/s)

17 Magnetized Atmosphere models Magnetized atmosphere models (Ho et al. 2008) => Optical/UV excess may depend on B models : B = 1-30 x 10^12 G, kt = ev, partially ionised hydrogen Brightness differs from BB but Rayleigh-Jeans behavior stays Wings of Proton-Cyclotron line can reproduce the spectral behavior of INSs partly => B_model << B_timing

18 Conclusions Counterparts of all seven INSs have been identified unambiguously All INSs show optical excess The Excess in some cases deviate significantly from the Rayleigh-Jeans regime Explanations ranging from different emission regions to mechanisms considered. None seems sufficient. More observations required to clearly characterize the optical/uv excess

19 Details & Back up slides

20 RCS models Resonant Cyclotron Scattering (Lyutikov & Gavriil 2006) => thermal photons matching cyclotron freq. of the NS magnetosphere undergo efficient repeated scatterings Photons are up-scattered => Thermal spectrum gets modified => produces BB+PL hard tail (see Rea et al. 2008) The model would retain Rayleigh-Jeans spectrum Would it produce optical/uv excess? (Also see Tong et al 2010, 2011)